1. Technical Field
The present invention relates to a field of backlight module techniques in liquid crystal displays, and in particularly to a backlight module and a method for detecting an electrostatic damage thereof.
2. Technical Background
Liquid crystal displays are widely used in various electronic communication products, and a backlight module is one of the important components in the liquid crystal display. At present, light emitting diodes (LEDs) are generally used as the light sources in the backlight module. Static electricity is likely generated in various manners in assembling the backlight module, e.g., during stages of producing the LEDs, welding the LEDs to a Flexible Printed Circuit (FPC) board, assembling an LED strip to the backlight module, and the like. During the entire production process from the LED chip production to the assembling of the whole electronic product, an electrostatic damage might be caused to the LEDs by operators, machines, materials and environments, and the prevention of the electrostatic damage has become an emphasis in the industry because the LED, which is a semiconductor element, is vulnerable to the static electricity since the PN junction thereof is directly exposed to the environment. When being applied by a normal operation current, an LED subjected to a severe electrostatic damage exhibits defects such as a current leakage or even cannot emit light, but an LED subjected to a slight electrostatic damage generally will not exhibit any abnormality. However, the LED subjected to a slight electrostatic damage already has a certain potential risk, and would exhibit defects such as darkened emitted light or an increased current leakage or even cannot emit light after the LED is subjected to a secondary electrostatic damage.
Since the electrostatic damage cannot be completely avoided so far from the production stages of Liquid Crystal Display Modules (LCMs), measures have been taken in the various production stages to detect whether the LED emits light normally, in order to remove the defective LED damaged by the static electricity. If damaged severely, the LED would become a failed light (that is, the LED is completely damaged, for example, by the static electricity and cannot operate normally), which may generally be found by directly detecting whether the LED normally emits light after the normal operation current is applied to the LED. As shown in FIG. 1, the LED strip or the backlight module (not shown) is connected to a normal power supply 3 through a lighting fixture 2, and an LED from the LED strip or the backlight module may be determined as a failed light or not by detecting whether the LED emits light normally.
In addition, an LED subjected to a slight electrostatic damage, if applied by the normal operation current, can also emit light normally and hence it is not possible to determine whether the LED has been subjected to the slight electrostatic damage. Nonetheless, the LED subjected to the slight electrostatic damage cannot emit light normally if a low current is applied thereto, thus, it is applicable to apply the low current to the LED in order to detect whether the LED has been slightly damaged by the static electricity. If any LED subjected to the slight electrostatic damage is not found, the LED would exhibit defects such as darkened emitted light or an increased current leakage or even cannot emit light, when the LED is subjected to a secondary electrostatic damage, as a result, the whole backlight module and the LCM cannot operate normally, resulting in lower yields and high production costs.
FIG. 2 shows the existing LED detection techniques for detecting whether an LED has been damaged by the static electricity. As shown, in Step S1, the low current-based detection is conducted on an individual LED chip to determine whether the individual LED chip emits light normally; in Step S2, the low current-based detection is conducted on an LED strip assembled by LED chips to determine whether the LED strip emits light normally; in Step S3, the low current-based detection is conducted on a backlight module assembled by LED strips to determine whether the backlight module emits light normally; but in Step S4, the low current-based detection can be conducted neither for the LCM assembled by the backlight modules, nor in the subsequent steps. The reason lies in that, after the backlight modules are assembled into the LCM, the current supplied to the LED is limited to a preset rated current having an unchangeable amount, which is a normal operation current instead of a low current, thus the low current-based detection cannot be conducted. However, in the step of assembling the backlight modules into the LCM as well as the subsequent steps, the electrostatic damage is inevitable, but the low current-based detection cannot be conducted for the LEDs in the LCMs, so that potential defective LEDs subjected to the electrostatic damage lead to a risk of the quality of the LCM.